1. Field of the Invention
Dynamic stabilization of the spine.
2. Description of Related Art
Physical discomfort from degenerative conditions of the spine such as disc disease, spinal stenosis, and spondylolisthesis affects a large segment of the population. Symptoms are related to compression of spinal nerves or nerve roots and may include intermittent neurogenic claudication, pain in back or legs, numbness, weakness and loss of balance. Conservative treatment may include rest, physical therapy, bracing, anti-inflammatory medications, analgesics, local anesthetic blocks and epidural steroid injections.
Treatment by spinal fusion is frequently offered to patients who suffer from these conditions. However, fused vertebrae have been associated with loss of mobility and deterioration of adjacent discal architecture due to increased strain and forces at such discs. Dynamic spinal stabililization of the spine is a treatment modality intended to overcome such deficiencies. Dynamic stabilization allows adjacent vertebrae to be stabilized through the use of, e.g., articulating structures, compressible structures and the like, to allow relative movement of adjacent vertebrae which are supported by such structures. In this manner, the aforementioned disadvantages of rigid fusion are avoided.
Dynamic stabilization typically involves rigid fastening of a dynamic stabilization implant (DSI) to one or more vertebrae using devices such as pedicle screws. In addition, DSIs are typically made of hard metals or plastics to provide adequate support between adjacent vertebrae under loaded conditions. In the case of rigid attachment, the point of attachment is usually subject to the brunt of the stress caused by normal movement. Moreover, such rigid attachment is a traumatic event for the bone itself. Use of rigid materials to construct the implant also provides for concentration of forces at the surface of the implant and can cause erosion of natural surfaces that contact the implant.
Surgical decompression with or without fusion is the standard surgical treatment for patients with moderate to severe lumbar spinal stenosis. Cervical, thoracic, and/or lumbar interspinous process decompression (IPD), also known as interspinous distraction or posterior spinal distraction, is a form of dynamic stabilization that has been proposed as a minimally invasive alternative to laminectomy and fusion. In IPD an interspinous distraction implant is inserted between the spinous processes through a small (e.g., 4-8 cm) incision. The device is intended to restrict painful motion while enabling otherwise normal motion. The implant theoretically enlarges the neural foramen, decompresses the cauda equina and acts as a spacer between the spinous processes to maintain the flexion of the spinal interspace.
There is continuing need for improved methods and devices for stabilizing compromised spinal architecture.